Solid-state laser element

ABSTRACT

To suppress the amplification of spontaneous emission light in a principal plane width direction to thereby suppress a gain in directions other than a beam axis direction and output a high-power laser, in a solid-state laser element of a plane waveguide type that causes a fundamental wave laser beam to oscillate in a beam axis direction in a laser medium of a flat shape and forms a waveguide structure in a thickness direction as a direction perpendicular to a principal plane of the flat shape in the laser medium, inclined sections  12  are provided on both sides of the laser medium, the inclined sections  12  inclining a predetermined angle to reflect spontaneous emission light in the laser medium to a principal plane side of the flat shape, the spontaneous emission light traveling in the beam axis direction and a principal plane width direction as a direction perpendicular to the thickness direction.

TECHNICAL FIELD

The present invention relates to a solid-state laser element that causesa laser beam to oscillate in a plane waveguide of a flat shape andoutputs a laser.

BACKGROUND ART

In apparatuses that display color images such as a printer and aprojection television, light sources for three colors R (red), G(green), and B (blue) are required as light sources. In recent years, asthese light sources, a wavelength conversion laser device (a laseroscillator) that converts, with a laser beam in a 900 nm band, a 1 μmband, or 1.3 μm band set as a fundamental wave laser beam, thefundamental wave laser beam into a second harmonic using a nonlinearmaterial (SHG, Second Harmonic Generation) is developed. To realize highconversion efficiency from the fundamental wave laser beam into a secondharmonic laser beam in the SHG, it is requested to increase the powerdensity of the fundamental wave laser beam on the nonlinear material andto convert the fundamental wave laser beam into a high-luminance laserbeam with less wavefront aberration.

A two-dimensional waveguide laser can realize the high conversionefficiency from the fundamental wave laser beam into the second harmoniclaser beam because the two-dimensional waveguide laser can increase thepower density of the fundamental wave laser beam. However, an increasein power is restricted because the two-dimensional waveguide laser has abreakage limit due to the high power density. Further, the increase inpower is restricted because the power of LD (Laser Diode) beams having ahigh beam quality in a two-dimensional direction (in the same plane asthe two-dimensional waveguide) connectable to the two-dimensionalwaveguide is generally low.

Therefore, a plane waveguide laser having a one-dimensional waveguidemay be used to increase the power of the second harmonic laser beam. Inthis plane waveguide laser, the increase in power is realized by causinga laser beam to oscillate in a direction perpendicular to a laser beamaxis in a flat surface (a direction perpendicular to principal planes ofa flat plate) according to a space mode, increasing a beam diameter ofthe laser beam in the direction perpendicular to the laser beam axis,and changing the laser beam to multiple beams. In such a plane waveguidelaser having the one-dimensional waveguide, LD beams as excitationsources only have to be coupled in a one-dimensional direction in theplane waveguide. Therefore, a high-power broad area LD can be used forthe plane waveguide laser having the one-dimensional waveguide. As aresult, a high-power laser beam can be obtained. Further, amulti-emitter LD in which light emitting points of LD beams are arrangedin the one-dimensional direction can be used for the plane waveguidelaser having the one-dimensional waveguide. Therefore, laser powerlarger than that obtained by using the broad area LD can be obtained(see Non-Patent Document 1).

Non-Patent Document 1: IEEE. J. Quantum Electronics Vol. 39 (2003), 495

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

However, in the conventional plane waveguide laser, when the beamdiameter of the laser beam is increased in the direction perpendicularto the laser beam axis (the thickness direction of the flat surface) orwhen the laser beam is changed to multiple beams, the size in the widthdirection of the flat surface has to be increased. When the size in thewidth direction of the flat surface is wide, because a gain in the widthdirection of the flat surface increases, there is a problem in thatparasitic oscillation occurs and high-power laser output cannot beobtained in some case.

Even when the parasitic oscillation does not occur, there is a problemin that a gain in the laser beam axis direction decreases because ofextraction of energy due to the amplification of spontaneous emissionlight and high-power laser output cannot be obtained.

The present invention has been devised in view of the above and it is anobject of the present invention to obtain a solid-state laser elementthat can output a high-power laser.

Means for Solving Problem

In order to solve the above mentioned problem and achieve the object, asolid-state laser element of a plane waveguide type according to thepresent invention that causes a fundamental wave laser beam to oscillatein a beam axis direction in a laser medium of a flat shape and forms awaveguide structure in a thickness direction as a directionperpendicular to a principal plane of the flat shape in the lasermedium, the solid-state laser element includes inclined sections thatare provided on both sides of the laser medium and inclined apredetermined angle to reflect spontaneous emission light in the lasermedium to a principal plane side of the flat shape, the spontaneousemission light traveling in the beam axis direction and a principalplane width direction as a direction perpendicular to the thicknessdirection.

EFFECT OF THE INVENTION

The solid-state laser element according to the present inventioninclines the inclined sections the predetermined angle to reflect thespontaneous emission light to the principal plane side of the flatshape. Therefore, there is an effect that it is possible to suppress theamplification of the spontaneous emission light in the principal planewidth direction and it is possible to suppress a gain in directionsother than the beam axis direction and output a high-power laser.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a top view of the configuration of a wavelength conversionlaser device according to a first embodiment.

FIG. 2 is a sectional view of the wavelength conversion laser deviceaccording to the first embodiment viewed from a side.

FIG. 3 is an a-a′ sectional view of FIGS. 1 and 2.

FIG. 4 is an enlarged view (1) of an A section shown in FIG. 3.

FIG. 5 is an enlarged view (2) of the A section shown in FIG. 3.

FIG. 6 is an enlarged view (3) of the A section shown in FIG. 3.

FIG. 7 is an enlarged view (4) of the A section shown in FIG. 3.

FIG. 8 is an enlarged view (5) of the A section shown in FIG. 3.

FIG. 9 is a top view of the configuration of a wavelength conversionlaser device according to a second embodiment.

FIG. 10 is a b-b′ sectional view of FIG. 9.

FIG. 11 is an enlarged view (1) of a B section shown in FIG. 10.

FIG. 12 is an enlarged view (2) of the B section shown in FIG. 10.

FIG. 13 is an enlarged view (3) of the B section shown in FIG. 10.

FIG. 14 is an enlarged view (4) of the B section shown in FIG. 10.

FIG. 15 is a top view of the configuration of a wavelength conversionlaser device according to a third embodiment.

FIG. 16 is an enlarged view of a C section shown in FIG. 15.

FIG. 17 is a c-c′ sectional view (1) of FIG. 15.

FIG. 18 is a c-c′ sectional view (2) of FIG. 15.

FIG. 19 is a c-c′ sectional view (3) of FIG. 15.

FIG. 20 is a sectional view of a wing section in which principal planesof groove wall surfaces are inclined in a latitudinal direction.

FIG. 21 is a sectional view of a wing section in which sides of groovesadjacent to each other are non-parallel to each other.

FIG. 22 is a top view of the configuration of a wavelength conversionlaser device according to a fourth embodiment.

EXPLANATIONS OF LETTERS OR NUMERALS

-   -   1 semiconductor laser    -   1 a active layer    -   2 heat sink    -   3, 3 b bonding agents    -   4, 4 b clads    -   5 laser media    -   5 a, 5 b, 7 a, 7 b end faces    -   6 optical axis    -   7 nonlinear material    -   11 substrate    -   12 inclined section    -   12 a mirror-finished inclined section    -   12 b roughed inclined section    -   13, 14 wing sections    -   13 a, 16, 20, 20 a to 20 e roughened surfaces    -   13 b, 15 reflection preventing films    -   13 b, 13 d absorbents    -   50 to 55, 60 to 64, 70 to 75, 80 solid-state laser elements    -   101 to 104 wavelength conversion laser devices    -   L second harmonic laser beam    -   N spontaneous emission light

BEST MODE(S) FOR CARRYING OUT THE INVENTION

Solid-state laser elements according to embodiments of the presentinvention are explained in detail below with reference to the drawings.The present invention is not limited by the embodiments.

First Embodiment

FIG. 1 is a top view of the configuration of a wavelength conversionlaser device according to a first embodiment of the present invention.FIG. 2 is a sectional view of the wavelength conversion laser deviceaccording to the first embodiment of the present invention viewed from aside. In FIGS. 1 and 2, a beam axis representing a laser oscillationdirection is indicated by an optical axis 6.

A wavelength conversion laser device 101 of a plane waveguide type is alaser oscillator in which inclined sections 12 are formed on sides (endfaces parallel to the optical axis 6) of a laser medium 5 to suppressparasitic oscillation and energy extraction due to the amplification ofspontaneous emission light in directions other than a laser beam axisdirection (the optical axis 6). The wavelength conversion laser device101 is used in light sources for a laser display device and an opticalmemory device in, for example, the optical information processing field.The wavelength conversion laser device 101 includes a semiconductorlaser 1, a nonlinear material (a nonlinear optical material) 7, and asolid-state laser element 50 as a main characteristic of the presentinvention.

The semiconductor laser 1 outputs a plurality of LD beams from aplurality of active layers 1 a. The semiconductor laser 1 emits an LDbeam in an array shape to output a plurality of LD beams and causes thesolid-state laser element 50 to perform multi-emitter oscillation. Thesolid-state laser element 50 is a plane waveguide element that causes afundamental wave laser beam to oscillate. The solid-state laser element50 includes a heat sink 2, a bonding agent 3, a clad (a low refractiveindex section) 4, and the laser medium 5. The nonlinear material (awavelength conversion element) 7 is an element that converts theoscillating fundamental wave laser beam into a second harmonic laserbeam L and emits a part of the converted second harmonic laser beam L.The nonlinear material 7 has a waveguide structure of a slab type.

In the following explanation, for convenience of the explanation, theoptical axis 6 is assumed as a z-axis direction, a directionperpendicular to principal planes of the wavelength conversion laserdevice 101 is assumed as a y-axis direction (a thickness direction), anda direction perpendicular to both the z axis and the y axis is assumedas an x-axis direction (in the laser medium 5, a principal plane widthdirection).

The semiconductor laser 1, the laser medium 5, and the nonlinearmaterial 7 respectively are formed in substantially rectangular flatshapes and disposed in the same plane such that principal planes of therespective flat shapes are parallel to the xz plane. The laser medium 5is disposed between the semiconductor laser 1 and the nonlinear material7 to be close to the semiconductor laser 1 on one side (an end face 5 aperpendicular to the z axis) of the laser medium 5 and close to thenonlinear material 7 on a side opposed to this side (an end face 5 bperpendicular to the z axis).

The nonlinear material 7 has an end face 7 a and an end face 7 bperpendicular to the optical axis 6. The end face 7 a is arranged closeto the end face 5 b of the laser medium 5. The end face 7 b of thenonlinear material 7 is an end face on a side where the second harmoniclaser beam L is emitted.

As explained above, in the wavelength conversion laser device 101, thesemiconductor laser 1, the solid-state laser element 50, and thenonlinear material 7 are disposed such that the emission surface of theLD beams of the semiconductor laser 1, the end faces 5 a and 5 b of thelaser medium 5, and the end faces 7 a and 7 b of the nonlinear material7 are parallel to one another.

The laser medium 5 (the solid-state laser element 50) according to thisembodiment has the inclined sections 12 on sides perpendicular to theend faces 5 a and 5 b (sides other than the end faces 5 a and 5 b of theflat shape) (both sides of the laser medium 5), respectively. Theinclined sections 12 have a predetermined angle with respect to adirection perpendicular to the principal planes (the upper surface andthe lower surface) of the laser medium 5 and extend in the optical axis6 direction. The inclined sections 12 reflect spontaneous emissionlight, which propagates through the laser medium 5 at an angle includinga component in the x-axis direction, to the upper surface side of thelaser medium 5.

The width in the x-axis direction of the semiconductor laser 1 issubstantially equal to the width in the x-axis direction on the lowersurface side of the laser medium 5. The semiconductor laser 1substantially uniformly outputs excitation beams in the x-axisdirection. The semiconductor laser 1 is, for example, a multi-emittersemiconductor laser in which a plurality of active layers 1 a thatoutput LD beams are arranged. When the semiconductor laser 1 is themulti-emitter semiconductor laser, in the semiconductor laser 1, theactive layers 1 a are arranged such that the active layers 1 a line upin the x-axis direction on a side close to the end face 5 a. In thiscase, because the semiconductor laser 1 outputs a plurality of LD beamsfrom the active layers 1 a, respective laser output beams are obtainedfrom the active layers 1 a arranged in the x-axis direction. The LDbeams output from the semiconductor laser 1 are made incident from theend face 5 a in an xz plane direction of the laser medium 5 (a directionperpendicular to the xy plane) (the optical axis 6 direction) andabsorbed by the laser medium 5. A heat sink for cooling (not shown inthe figure) can be bonded to the semiconductor laser 1 according tonecessity.

The end face 5 a of the laser medium 5 is a total reflection film thatreflects the fundamental wave laser beam. The end face 5 b of the lasermedium 5 is a reflection preventing film that transmits the fundamentalwave laser beam. The end face 7 a of the nonlinear material 7 is anoptical film (a partial reflective film) that transmits the fundamentalwave laser beam and reflects the second harmonic laser beam L. The endface 7 b of the nonlinear material 7 is an optical film (a partialreflective film) that reflects the fundamental wave laser beam andtransmits the second harmonic laser beam L. The total reflection film,the reflection preventing film, and the optical film are manufacturedby, for example, laminating dielectric thin films. When the excitationbeams output from the semiconductor laser 1 are made incident from theend face 5 a of the laser medium 5, the total reflection film of the endface 5 a is an optical film that transmits the excitation beams andreflects the fundamental wave laser beam.

The laser medium 5 has, for example, the thickness of several to severaltens micrometers in the y-axis direction and the width (the principalplane width of the upper surface and the principal panel width of thelower surface) of several hundreds micrometers to several millimeters inthe x-axis direction. As the laser medium 5, a general solid-state lasermaterial can be used. The laser medium 5 is, for example, Nd:YAG,Nd:YLF, Nd:Glass, Nd:YVO4, Nd:GdVO4, Yb:YAG, Yb:YLF, Yb:KGW, Yb:KYW,Er:Glass, Er:YAG, Tm:YAG, Tm:YLF, Ho:YAG, Ho:YLF, Tm,Ho:YAG, Tm,Ho:YLF,Ti:Sapphire, or Cr:LiSAF.

A clad 4 has a refractive index smaller than that of the laser medium 5and is bonded to the lower surface side of the laser medium 5 on oneplane parallel to the xz plane of the laser medium 5 (the upper surfaceof the clad 4). The clad 4 is manufactured by, for example, a method ofvapor-depositing a film containing an optical material as a row materialon the laser medium 5 or a method of optically bonding the opticalmaterial to the laser medium with optical contact, diffusion bonding, orthe like.

The heat sink 2 contains a material having large thermal conductivityand is bonded to the clad 4 via the bonding agent 3 on the lower surfaceside of the clad 4. The bonding agent 3 discharges heat generated in thelaser medium 5 to the heat sink 2 via the clad 4. As this bonding agent3, for example, metal solder, an optical adhesive, or a thermalconduction adhesive is used. In the clad 4, a surface (the bottomsurface) opposed to the surface to which the laser medium 5 is bondedcan be metalized (a metal film can be deposited on the surface) toincrease the strength of the bonding with the bonding agent 3. When theheat sink 2 is formed of an optical material, the clad 4 and the heatsink 2 can be directly bonded by, for example, optical contact,diffusion bonding, or the like. Consequently, the heat sink 2, thebonding agent 3, the clad 4, and the laser medium 5 form a laminatedstructure in the y-axis direction.

As the nonlinear material 7, a general wavelength converting materialcan be used. As the nonlinear material 7, for example, KTP, KN, BBO,LBO, CLBO, LiNbO3, or LiTaO3 is used. If MgO added LiNbO3, MgO addedLiTaO3, stoichiometric LiNbO3, or stoichiometric LiTaO3 robust againstoptical damage is used as the nonlinear material 7, highly efficientwavelength conversion is possible because the power density of anincident fundamental wave laser beam can be increased. Further, if MgOadded LiNbO3, MgO added LiTaO3, stoichiometric LiNbO3, stoichiometricLiTaO3, or KTP having a periodic reversal polarization structure is usedas the nonlinear material 7, more highly accurate wavelength conversionthan that realized by MgO added LiNbO3 and the like is possible becausea nonlinear constant is large.

FIG. 3 is an a-a′ sectional view of FIGS. 1 and 2. As shown in FIG. 3,the laser medium 5 forming the waveguide structure is extended in theprincipal plane width direction of the laser medium 5. The inclinedsections 12 are formed at ends (inclined surfaces) of the extended lasermedium 5.

In the laser medium 5, the principal plane width on the upper surfaceside is larger than the principal plane width on the lower surface side.The a-a′ section of the laser medium 5 is formed in a trapezoidal shape.In other words, the principal plane width of the upper surface of thelaser medium 5 is formed to be larger than the principal plane width ofthe lower surface of the laser medium 5 and the width in the x-axisdirection of the principal planes of the heat sink 2, the bonding agent3, and the clad 4. The inclined sections 12 are inclined from adirection perpendicular to the principal planes of the laser medium 5such that the principal plane width gradually increases from the lowersurface side to the upper surface side of the laser medium 5. Therefore,the inclined sections 12 form a predetermined angle other than 90degrees with the upper surface and the lower surface of the laser medium5 (e.g., 30 degrees with the upper surface). Consequently, the lasermedium 5 is formed as a trapezoidal pole with the end faces 5 a and 5 bforming a trapezoid and a column axis being parallel to the optical axis6.

In the explanation with reference to FIG. 3, the principal plane widthon the upper surface side of the laser medium 5 is larger than theprincipal plane width on the lower surface side thereof. However, theprincipal plane width on the lower surface side of the laser medium 5can be set larger than the principal plane width on the upper surfaceside thereof. In this case, the principal plane width on the uppersurface side of the laser medium 5 is set larger than the principalplane width of the clad 4. The inclined sections 12 are not limited tostraight lines and can be curved lines.

An operation procedure of the wavelength conversion laser device 101 isexplained. An excitation beam from the semiconductor laser 1 madeincident on the end face 5 a of the laser medium 5 is absorbed by thelaser medium 5 and generates a gain with respect to the fundamental wavelaser beam in the inside of the laser medium 5. The fundamental wavelaser beam oscillates, with the gain generated in the laser medium 5,between the end face 5 a of the laser medium 5 and the end face 7 a ofthe nonlinear material 7 perpendicular to the optical axis 6.

A crystallographic axis angle, temperature, a period of periodicreversal polarization, and the like of the nonlinear material 7 areoptimized such that the fundamental wave laser beam is converted intothe second harmonic laser beam L by a nonlinear effect. Therefore, whenthe fundamental wave laser beam oscillating between the end face 5 a andthe end face 7 b is made incident on the nonlinear material 7, a part ofthe fundamental wave laser beam is converted into the second harmoniclaser beam L and output to the outside from the end face 7 b.

The fundamental wave laser beam remaining in the nonlinear material 7without being converted into the second harmonic laser beam L is totallyreflected on the end face 7 b, passes through the nonlinear material 7again, and is converted into the second harmonic laser beam L. Thesecond harmonic laser beam L generated by converting a part of theremaining fundamental wave laser beam is totally reflected on the endface 7 a and output to the outside from the end face 7 b.

The laser medium 5 has the thickness in the y-axis direction aboutseveral times to several tens times as large as the wavelength of alaser beam. Because the laser medium 5 is sandwiched by the clad 4 andthe air having refractive indexes smaller than that of the laser medium5, the laser medium 5 operates as a waveguide with the fundamental wavelaser beam contained in the laser medium 5 having the high refractiveindex. Consequently, the laser medium 5 forms a waveguide structure inthe y-axis direction. The fundamental wave laser beam in the lasermedium 5 selectively oscillates in a predetermined mode (a laseroscillation mode) of the waveguide. The mode of the waveguide can bearbitrarily set by adjusting the refractive index of the clad 4 and thethickness in the y-axis direction of the laser medium 5. Therefore, inthe mode of the waveguide, high luminance oscillation can be realized byguiding only a low-order mode or a single mode.

In the laser medium 5, a refractive index distribution also occurs inthe y-axis direction because of a heat distribution caused by exhaustheat. However, if a refractive index difference between the clad 4 andthe laser medium 5 and a refractive index difference between the air andthe laser medium 5 are sufficiently large compared with a refractiveindex change due to the heat distribution, the mode of the waveguide ispredominant and the influence due to the heat in the y-axis directioncan be neglected. In this embodiment, the clad 4 and the laser medium 5in which the refractive index difference between the clad 4 and thelaser medium 5 and the refractive index difference between the air andthe laser medium 5 are values sufficiently larger than the refractiveindex change due to the heat distribution are used in the wavelengthconversion laser device 101.

In the nonlinear material 7, the upper surface and the lower surfaceperpendicular to the y axis are sandwiched by the air and a clad (notshown in the figure). The air and the clad have refractive indexes thatare small compared with that of the nonlinear material 7. The nonlinearmaterial 7 operates as a waveguide in the y-axis direction in the samemanner as the laser medium 5 because the thickness thereof in the y-axisdirection is about several times to several tens times as large as thewavelength of the laser beam. Consequently, the laser medium 5 and thenonlinear material 7 set the laser beam in the oscillation mode.

When the nonlinear material 7 absorbs the laser beam and generates heat,the heat absorbed in the nonlinear material 7 can be discharged to theoutside of nonlinear material 7 by bonding a heat sink to the lowersurface of the nonlinear material 7 or the clad (not shown in thefigure) bonded to the nonlinear material 7.

For example, when the heat sink is directly bonded to the nonlinearmaterial 7, the y-axis direction of the nonlinear material 7 is allowedto be used as a waveguide by using an optical material having arefractive index smaller than that of the nonlinear material 7 as a heatsink material or using a bonding agent (e.g., an optical adhesive)having a refractive index smaller than that of the nonlinear material 7.In other words, the nonlinear material 7 and the solid-state laserelement 50 are caused to form a waveguide structure in the verticaldirection (the y-axis direction).

A mode in the y-axis direction of laser oscillation in the z-axisdirection in the laser oscillator (from the end face 5 a of the lasermedium 5 to the end face 7 b of the nonlinear material 7) is selectivelyset according to a mode of the waveguide of the laser medium 5 and amode of the waveguide of the nonlinear material 7. Each of the mode ofthe waveguide of the laser medium 5 and the mode of the waveguide of thenonlinear material 7 can be arbitrarily set according to the thicknessin the y-axis direction of the laser medium 5 and a refractive indexdifference between the laser medium 5 and the clad 4. Therefore, in themode of the waveguide of the laser medium 5 and the mode of thewaveguide of the nonlinear material 7, high luminance oscillation can berealized by guiding only a low-order mode or a single mode.

The waveguide mode of the laser medium 5 and the waveguide mode of thenonlinear material 7 can be the same waveguide mode or can be differentwaveguide modes. For example, if one waveguide mode is set as amultimode and the other waveguide mode is set as a single mode, becausea mode of laser oscillation is restricted by a lowest order mode, alaser can selectively oscillate in the single mode.

A mode in the x-axis direction of laser oscillation in the z-axisdirection in the laser oscillator is set in a spatial mode without beingselected according to a waveguide because the principal plane width ofthe laser medium 5 and the width in the x-axis direction of thenonlinear material 7 are sufficiently large compared with thewavelengths of the fundamental wave laser beam and the second harmoniclaser beam L.

Spontaneous emission light of the laser medium 5 is explained. The lasermedium 5 excited by a LD beam emits spontaneous emission light in alldirections and resonates in the optical axis 6 direction to performlaser oscillation. Therefore, if there is unintended parasiticoscillation in directions other than the optical axis 6 direction orextraction of energy due to the amplification of the spontaneousemission light, a gain in the optical axis 6 direction decreases andlaser output power falls.

For example, in spontaneous emission light propagating through the lasermedium 5 at an angle including a component in the x-axis direction,components that satisfy all reflection angles on all sides in the lasermedium 5 and all boundary surfaces (the upper surface and the lowersurface) of the laser medium 5 may be amplified propagating through thewaveguide at the angle including the component in the x-axis direction.When the components that satisfy all the reflection angles increase, again received by spontaneous emission light propagating in a directionincluding the component in the x-axis direction increases. Therefore,parasitic oscillation that is totally reflected in the inside of thelaser medium 5 tends to occur. In particular, when a semiconductor laserhaving large width in the x-axis direction or a semiconductor laser inwhich a plurality of active layers 1 a are arranged is used as anexcitation source, parasitic oscillation that is totally reflected inthe inside of the laser medium 5 tends to occur.

Even when a parasitic oscillation threshold value is not reached, a gainin the optical axis 6 direction decreases because of extraction ofenergy due to the amplification of the spontaneous emission lightpropagating in the direction including the x-axis direction in the lasermedium 5 and high-power laser output cannot be obtained.

In this way, the spontaneous emission light generated in the lasermedium 5 is amplified by repeating total reflection on the sides and thelike of the laser medium 5. On the sides of the laser medium 5, when thesides of the laser medium 5 are perpendicular to the principal planes ofthe laser medium 5, the spontaneous emission light tends to satisfy allreflection angles on the sides of the laser medium. Therefore, theextraction of energy due to the amplification of the spontaneousemission light can be suppressed by inclining the sides of the lasermedium 5 by a predetermined angle from the direction perpendicular tothe principal planes of the laser medium 5.

In this embodiment, the inclined sections 12 are formed on the sides ofthe laser medium 5. Therefore, a reflection angle of the spontaneousemission light reflected on the inclined sections 12 increases.Consequently, because the spontaneous emission light deviates from thetotal reflection condition for the waveguide and leaks to the outside ofthe waveguide, the amplification of the spontaneous emission light inthe x-axis direction decreases. Therefore, even when the semiconductorlaser 1 having large width in the x-axis direction or the semiconductorlaser 1 in which a plurality of active layers 1 a are arranged is usedas an excitation source, the parasitic oscillation and the extraction ofenergy due to the amplification of the spontaneous emission lightdecrease and the decrease in the gain in the optical axis 6 direction isreduced. Consequently, the wavelength conversion laser device 101 cangenerate a high-power laser beam in the optical axis 6 direction.

FIG. 4 is an enlarged view (1) of an A section shown in FIG. 3. FIG. 5is an enlarged view (2) of the A section shown in FIG. 3. In FIG. 4, theA section shown in FIG. 3 is shown as a solid-state laser element 51. InFIG. 5, the A section shown in FIG. 3 is shown as a solid-state laserelement 52.

In the solid-state laser element 51 shown in FIG. 4, the section of theinclined section 12 is formed as a mirror-finished inclined section 12 athat mirror-reflects spontaneous emission light N. In this case, thespontaneous emission light N propagating in the laser medium 5 at theangle including the component in the x-axis direction (hereinafterreferred to as spontaneous emission light N in the x-axis direction) isreflected on the mirror-finished inclined section 12 a and travels tothe upper surface side of the laser medium 5. Consequently, parasiticoscillation and the spontaneous emission light N to be amplifieddecrease.

In the solid-state laser element 52 shown in FIG. 5, the inclinedsection 12 is formed as a roughened inclined section 12 b that transmitsa part of the spontaneous emission light N while diffusing the same andreflects a part of the spontaneous emission light N while diffusing thesame. In this case, a part of the spontaneous emission light N in thex-axis direction is reflected on the roughened inclined section 12 bwhile being diffused and travels to the upper surface side of the lasermedium 5. Further, a part of the spontaneous emission light N in thex-axis direction is transmitted through the roughened inclined section12 b while being diffused and travel to the outer side of the lasermedium 5. The part of the spontaneous emission light N diffused by theroughened inclined section 12 b deviates from the total reflectioncondition for the waveguide. Therefore, parasitic oscillation and thespontaneous emission light N to be amplified decrease.

In the explanation with reference to FIGS. 4 and 5, the solid-statelaser elements 51 and 52 do not include a substrate and the like on theupper surface side of the laser medium 5. However, the solid-state laserelements 51 and 52 can include a substrate and the like.

FIGS. 6 to 8 are enlarged views (3) to (5) of the A section shown inFIG. 3. In FIG. 6, the A section shown in FIG. 3 is shown as asolid-state laser element 53. In FIG. 7, the A section shown in FIG. 3is shown as a solid-state laser element 54. In FIG. 8, the A sectionshown in FIG. 3 is shown as a solid-laser element 55. In the solid-statelaser elements 53 to 55 shown in FIGS. 6 to 8, a clad 4 b is disposed onthe upper surface side of the laser medium 5 (a reflecting directionside of spontaneous emission light by the inclined section 12) and theclad 4 b and a substrate 11 are bonded via a bonding agent 3 b.Consequently, in the solid-state laser elements 53 to 55 shown in FIGS.6 to 8, the substrate 11 is bonded to the laser medium 5 via apredetermined bonding surface.

The solid-state laser element 53 shown in FIG. 6 has a configuration inwhich the substrate 11 and the like are disposed on the upper surfaceside of the laser medium 5 (the laser medium 5 having themirror-finished inclined section 12 a) shown in FIG. 4. A reflectionpreventing film 15 is disposed on the upper surface (an opposed surfaceopposed to the bonding surface with the laser medium 5) of the substrate11.

In the solid-state laser element 53, the spontaneous emission light N inthe x-axis direction is reflected on the mirror-finished inclinedsection 12 a and travels to the reflection preventing film 15. Thespontaneous emission light N traveling to the reflection preventing film15 is transmitted through the reflection preventing film 15 and exits tothe outside of the solid-state laser element 53. Consequently, parasiticoscillation and the spontaneous emission light N to be amplifieddecrease.

The solid-state laser element 54 shown in FIG. 7 has a configuration inwhich the substrate 11 and the like are disposed on the upper surfaceside of the laser medium 5 (the laser medium 5 having the roughenedinclined section 12 b) shown in FIG. 5. The reflection preventing film15 is disposed on the upper surface of the substrate 11.

In the solid-state laser element 54, a part of the spontaneous emissionlight N in the x-axis direction is reflected on the roughened inclinedsection 12 b while being diffused and travels to the reflectionpreventing film 15. The spontaneous emission light N traveling to thereflection preventing film 15 is transmitted through the reflectionpreventing film 15 and exits to the outside of the solid-state laserelement 54. Consequently, parasitic oscillation and the spontaneousemission light N to be amplified decrease.

The solid-state laser element 55 shown in FIG. 8 has a configuration inwhich the substrate 11 and the like are disposed on the upper surfaceside of the laser medium 5 shown in FIG. 5. The upper surface of thesubstrate 11 is formed as a roughened surface 16. In the solid-statelaser element 55, a part of the spontaneous emission light N in thex-axis direction is reflected on the roughened inclined section 12 bwhile being diffused and travels to the roughened surface 16. Theroughened surface 16 transmits a part of the spontaneous emission lightN while diffusing the same and reflects a part of the spontaneousemission light N while diffusing the same. The spontaneous emissionlight N transmitted through the roughened surface 16 exits to theoutside of the solid-state laser element 55. Consequently, parasiticoscillation and the spontaneous emission light N to be amplifieddecrease.

The roughened surface 16 can be applied to the solid-state laser element51 shown in FIG. 4. In FIGS. 6 to 8, a part (a triangular pole) on thelower surface side of the substrate 11 is shaved off and a cut surfaceof the substrate 11 exposed as a result of the shaving-off and a slopeof the inclined section 12 line up on the same plane. However, the parton the lower surface side of the substrate 11 does not have to be shavedoff. The ends in the x-axis direction of the clad 4 b and the bondingagent 3 b can be shaved off to be parallel to the slope of the inclinedsection 12 or do not have to be shaved off.

In the explanation with reference to FIGS. 6 to 8, the reflectionpreventing film 15 and the roughened surface 16 are disposed on theupper surface of the substrate 11. However, the reflection preventingfilm 15 and the roughened surface 16 can be disposed on the sides, thebottom surface, or the cut surface of the substrate 11.

An inclination angle (a side angle range) of the inclined section 12with respect to the principal planes of the laser medium 5 is explained.A condition under which the spontaneous emission light N parallel to theprincipal planes of the laser medium 5 (components propagating through acore in parallel to the flat surface of the waveguide) is transmittedthrough the inclined section 12 without being totally reflected by theinclined section 12 is indicated by Formula (1).

$\begin{matrix}{\theta_{3} < {{Sin}^{1}\frac{1}{n_{2}}}} & (1)\end{matrix}$

θ₃ represents an inclination angle of the inclined section 12 withrespect to the direction perpendicular to the principal planes of thelaser medium 5 and n₂ represents a refractive index of the laser medium5. For example, when n₂=2.2, in a range in which the inclination angleθ₃ satisfies θ₃<27°, the spontaneous emission light N parallel to theprincipal planes of the laser medium 5 is transmitted through theinclined section 12.

However, even when the transmission condition is satisfied, in somecase, the spontaneous emission light N is Fresnel-reflected according toa refractive index difference between the laser medium 5 and the clad 4.A reflection amount R of the Fresnel reflection is represented byR=((n₂−1)/(n₂+1))².

A condition under which the spontaneous emission light N parallel to theprincipal planes of the laser medium 5 is reflected on the inclinedsection 12 and then transmitted through the clad 4 without beingreflected by the clad 4 is indicated by Formula (2).

$\begin{matrix}{{\frac{1}{2}\left( {90 - \theta_{m}} \right)} < \theta_{3} < {\frac{1}{2}\left( {90 + \theta_{m}} \right)}} & (2)\end{matrix}$

θ_(m) represents a critical angle of the laser medium 5 and the clad 4.n1 represents a refractive index of the clad 4. n₂ represents arefractive index of the laser medium 5. θ_(m) is represented asθ_(m)=Sin⁻¹(n₁/n₂). For example, when n₁=1.96 and n₂=2.2, the criticalangle of the laser medium 5 and the clad 4 is θ_(m)=63°.

Therefore, if the inclination angle θ₃ is set in a range of13.5°<θ₃<76.5°, the spontaneous emission light N parallel to theprincipal planes of the laser medium 5 is reflected on the inclinedsection 12 and then transmitted through the clad 4 without being totallyreflected on the clad 4.

According to Formula (1) and Formula (2), the spontaneous emission lightN parallel to the principal planes of the laser medium 5 satisfies acondition of Formula (3).

$\begin{matrix}{{\frac{1}{2}\left( {90 - {{Sin}^{- 1}\frac{n_{1}}{n_{2}}}} \right)} < \theta_{3} < {{Sin}^{- 1}\frac{1}{n_{2}}}} & (3)\end{matrix}$

For example, when n₁=1.96 and n₂=2.2, if the inclination angle θ₃ is setin a range of 13.5°<θ₃<27°, a part of the spontaneous emission light Nparallel to the principal planes of the laser medium 5 passes throughthe inclined section 12 and a part thereof is reflected on the inclinedsection 12 according to the Fresnel reflection. The reflected componentis transmitted through the clad 4 without being totally reflected on theclad 4.

A condition under which the spontaneous emission light N forming aradiation angle θ_(a) with respect to the principal planes of the lasermedium 5 (components propagating through the core at the radiation angleθ_(a) with respect to the flat surface of the waveguide) is transmittedthrough the inclined section 12 without being totally reflected on theinclined section 12 is indicated by Formula (4).

$\begin{matrix}{{\theta_{3} \pm \theta_{a}} < {{Sin}^{- 1}\frac{1}{n_{2}}}} & (4)\end{matrix}$

When a maximum radiation angle at which the spontaneous emission light Ncan propagate through the core is represented as θ_(a-max),θ_(a-max)=90−Sin⁻¹(n₁/n₂). For example, when n₁=1.96 and n₂=2.2,θ₃<0.02° with respect to the radiation angle θ_(a-max). Therefore, theinclined section 12 needs an angle substantially perpendicular to theprincipal planes of the laser medium 5.

A condition under which the spontaneous emission light N forming theradiation angle θ_(a) with respect to the principal planes of the lasermedium 5 is reflected on the inclined section 12 and then transmittedthrough the clad 4 without being totally reflected on the clad 4 isindicated by Formula (5).

$\begin{matrix}{{\frac{1}{2}\left( {90 - \theta_{m}} \right)} < {\theta_{3} \pm \theta_{a}} < {\frac{1}{2}\left( {90 + \theta_{m}} \right)}} & (5)\end{matrix}$

θ_(a) satisfies a condition θ_(a)=90−θ_(m). For example, when n₁=1.96and n₂=2.2, θ_(m)=63°. As a range of an inclination angle, a condition13.5°<θ₃±27°<76.5° is obtained. However, θ₃ satisfying this conditionexceeds a range of 0° to 90°. Therefore, there is no condition (an anglecondition for the inclined section 12) for transmitting all components(radiation angle components) propagated at ±θ_(a-max) from the lasermedium 5 via the inclined section 12 and the clad 4. Therefore, it isdesirable to set the inclination angle θ₃ to 45° that is in the centerof the angle range of the inclination angle.

In this way, to reduce return beams into the laser medium 5 (thespontaneous emission light N reflected in the core) in both the inclinedsection 12 and the clad 4, a condition for transmitting a center valuein a range of a radiation angle for allowing the spontaneous emissionlight N to propagate through the laser medium 5 (parallel beams parallelto the principal planes of the laser medium 5) is the best. Therefore,when the inclination angle satisfies the condition of Formula (3),unnecessary spontaneous emission light N can be discharged to theoutside of the laser medium 5 at a highest rate. To reduce the returnbeams into the laser medium 5 only in the clad 4, it is desirable to setthe inclination angle to θ₃=45° in the center of the angle range ofFormula (5).

Here, a blue laser in which Nd:YVO4 or Nd:GdVO4 is used as the lasermedium 5 is explained. In the wavelength conversion laser device 101 ofthe waveguide type shown in FIG. 1, linear polarized light due to laseroscillation is often obtained according to a gain/loss ratio in thewaveguide mode. Therefore, even when linear polarized light is requestedfor a fundamental wave laser beam in wavelength conversion, ahigh-luminance fundamental wave laser beam suitable for the wavelengthconversion can be output. Further, if a laser medium (Nd:YVO4 orNd:GdVO4) having a different gain according a crystallographic axisdirection is used as the laser medium 5, linear polarized lightoscillation in a direction in which a gain is high can be easilyobtained. Therefore, even when linear polarized light is requested in afundamental wave laser beam in the wavelength conversion, ahigh-luminance fundamental wave laser beam suitable for the wavelengthconversion can be output.

The blue laser can be obtained by using a laser medium that outputs alaser beam having a wavelength in a 900 nm band as a fundamental waveand wavelength-converting the fundamental wave into a second harmonic.Because Nd:YVO4 or Nd:GdVO4 has a gain band near 914 nanometers, a bluelaser near 457 nanometers can be obtained by using Nd:YVO4 or Nd:GdVO4as the laser medium 5.

In Nd:YVO4 and Nd:GdVO4, a wavelength with a highest gain is a 1064 nmband. There is also a gain in a wavelength of a 1.3 μm band. Therefore,to cause a fundamental wave in a 914 nm band to efficiently oscillate,it is necessary to suppress extraction of energy due to laseroscillation, parasitic oscillation, and the amplification of spontaneousemission light in an unintended direction in the 1064 nm band having thehighest gain and oscillation in the 1.3 μm band.

To suppress laser oscillation in the 1064 nm band and the 1.3 μm band inthe optical axis 6 direction, the total reflection film (the end face 5a) that reflects the fundamental wave laser beam of the laser medium 5is, for example, a film that totally reflects a wavelength in the 914 mband as a fundamental wave of the blue laser and transmits wavelengthsin the 1064 nm band and the 1.3 μm band. The reflection preventing film(the end face 5 b) that transmits the fundamental wave laser beam is,for example, a film that transmits all the wavelengths in the 914 nmband, the 1064 nm band, and the 1.3 μm band. Further, the optical film(the end face 7 a) that transmits the fundamental wave laser beam of thenonlinear material 7 and reflects the second harmonic laser beam L is,for example, a film that transmits all the wavelengths in the 914 nmband, the 1064 nm band, and the 1.3 μm band. The optical film (the endface 7 b) that reflects the fundamental wave laser beam and transmitsthe second harmonic laser beam L is, for example, a film that totallyreflects the wavelength in the 914 nm band and transmits the wavelengthsin the 1064 nm band and the 1.3 μm band.

With such a film configuration of the laser medium 5, the wavelengthconversion laser device 101 can perform, while suppressing laseroscillation in the 1064 nm band and the 1.3 μm band in the optical axis6 direction, laser oscillation in the 914 nm band between the totalreflection film (the end face 5 a) that reflects the fundamental wavelaser beam and the optical film (the end face 7 b) that reflects thefundamental wave laser beam and transmits the second harmonic laser beamL. Consequently, a blue laser in a 457 nm band converted into a secondharmonic by the nonlinear material 7 is output.

For example, when the second harmonic is generated by using the 1064 nmband as the wavelength of the fundamental wave, because the secondharmonic laser beam L in a 532 nm band is output from the nonlinearmaterial 7, a green laser can be obtained. In this case, a laseroscillation threshold value is low because the wavelength in the 1064 nmband has a high gain. Laser oscillation in the optical axis 6 directioncan be easily performed. Because the laser oscillation threshold valueis low, a gain remaining in the laser medium 5 is small. Parasiticoscillation in an unintended direction other than the optical axis 6direction, extraction of energy due to amplification spontaneousemission light, and laser oscillation in other wavelengths such as the914 nm band and the 1.3 μm band in the optical axis 6 direction hardlyoccur. Therefore, even when an increase in power of a laser beam isrealized by increasing a beam diameter in the y direction or changingthe laser beam into multiple beams in the plane waveguide laser,parasitic oscillation of a laser beam propagating at the angle includingthe x-axis direction and extraction of energy due to the amplificationof spontaneous emission light also hardly occur. Therefore, a high-powergreen laser can be easily obtained.

When the fundamental wave is the 914 nm band having a low gain, a laseroscillation threshold value is high because the gain is low. Therefore,even when laser oscillation in the 1064 nm band and the 1.3 μm band inthe optical axis 6 direction is suppressed by the film configuration ofthe laser medium 5, because the laser oscillation threshold value ishigh, a gain in an unintended angle direction including the x-axisdirection is also high. Unintended parasitic oscillation and theamplification of spontaneous emission light may occur. Further, when abeam width is increased in the x direction or a laser beam is changed tomultiple beams in the plane waveguide laser, a gain in the angledirection including the x-axis direction increases and parasiticoscillation tends to occur. Even when the parasitic oscillation does notoccur, extraction of energy due to the amplification of spontaneousemission light increases because a propagation length of the laser beamis large. A gain in the optical axis 6 direction is reduced. Therefore,the power of the fundamental wave laser in the 914 nm band in theoptical axis 6 direction falls and the power of the blue laser of thesecond harmonic may also fall.

In this embodiment, because the inclined sections 12 are formed on thesides of the laser medium 5, spontaneous emission light in the x-axisdirection can be suppressed. As a result, parasitic oscillation of thespontaneous emission light oscillating at an angle (an unintended angle)including the x-axis direction can be suppressed. Even when theparasitic oscillation does not occur, extraction of energy due to theamplification of the spontaneous emission light can be suppressed.

Therefore, even when laser oscillation with the 914 nm band having thehigh laser oscillation threshold value set as a fundamental wave isperformed, because a fall in a gain due to extraction of energy issmall, a high-power fundamental wave laser beam can be obtained. Becausethe laser power of the fundamental wave is high, wavelength conversionefficiency in the nonlinear material 7 is high. A blue laser L as thehigh-power second harmonic laser beam L can be obtained.

In the explanation with reference to FIG. 1 and the like, the wavelengthconversion laser device 101 adopts an internal wavelength conversionsystem for arranging the nonlinear material 7 in the oscillator of afundamental wave and causing the fundamental wave to oscillate betweenthe total reflection film (the end face 5 a) of the laser medium 5 andthe optical film (the end face 7 b) of the nonlinear material 7.However, the wavelength conversion laser device 101 can performwavelength conversion according to an external wavelength conversionsystem. In the external wavelength conversion system, a wavelengthconversion element is set on the outside of a resonator. For example, apartial reflection film that reflects a part of a fundamental wave laserbeam is formed on one end face of the laser medium 5 (which is a sideopposed to the end face 5 a and is an end face on the side close to thenonlinear material 7). The wavelength conversion laser device 101performs laser oscillation of the fundamental wave laser beam on boththe end faces (the end face 5 a and the partial reflection film) of thelaser medium 5. In this case, a fundamental wave output from the lasermedium 5 is made incident on the nonlinear material 7, wavelengthconversion is performed in the nonlinear material 7, and the secondharmonic laser beam L is obtained.

Even in such an external wavelength conversion system, as in theinternal wavelength conversion system, parasitic oscillation in anunintended direction can be suppressed and extraction of energy due tothe amplification of spontaneous emission light in an unintendeddirection can be suppressed. Therefore, even if the wavelengthconversion laser device 101 adopts the external wavelength conversionsystem, a high-power fundamental wave in the optical axis 6 directioncan be obtained. As a result, a high-power second harmonic laser L canbe obtained.

As explained above, according to the first embodiment, the inclinedsections 12 reflect the spontaneous emission light N in the x-axisdirection to the upper surface side of the laser medium 5. Therefore,the parasitic oscillation in directions other than the optical axis 6direction and the extraction of energy due to the amplification of thespontaneous emission light N decrease and the decrease in the gain inthe optical axis 6 direction is reduced. Therefore, the solid-statelaser element 50 can output a high-power laser.

Second Embodiment

Next, a second embodiment of the present invention is explained withreference to FIGS. 9 to 14. In the second embodiment, wing sections 13explained later are disposed on the outer sides in the x-axis directionof the clad 4 as means for allowing the spontaneous emission light N toescape to the outside of the laser medium 5 (transmission or absorption)or means for diffusing the spontaneous emission light N.

FIG. 9 is a top view of the configuration of a wavelength conversionlaser device according to the second embodiment of the presentinvention. A sectional configuration of a wavelength conversion laserdevice 102 according to the second embodiment viewed from a side is thesame as that of the wavelength conversion laser device 101 according tothe first embodiment shown in FIG. 2. Components that attain functionssame as those of the wavelength conversion laser device 101 according tothe first embodiment shown in FIG. 1 among components shown in FIG. 9are denoted by the same numerals and redundant explanation of thecomponents is omitted.

The wavelength conversion laser device 102 of the plane waveguide typeincludes the semiconductor laser 1, the nonlinear material 7, and asolid-state laser element 60 as a main characteristic of the presentinvention. The wavelength conversion laser device 102 performs laseroscillation and performs wavelength conversion for a fundamental wavelaser beam according to processing same as that performed by thewavelength conversion laser device 101. In this embodiment, the width inthe x-axis direction of the laser medium 5 is set larger than the widthin the x-axis direction of the clad 4. A pair of wing sections 13 areformed on both the outer sides in the x-axis direction of the clad 4.

The laser medium 5 (the solid-state laser element 60) according to thisembodiment has the wing sections 13 near sides perpendicular to the endfaces 5 a and 5 b, respectively. The wing sections 13 are formed in aflat shape parallel to the xz plane. A principal plane thereof viewedfrom the upper surface is formed in a substantially rectangular shape.The length in the optical axis 6 direction of the wing sections 13 issubstantially the same as the length in the optical axis 6 direction ofthe principal planes of the laser medium 5. The width in the x-axisdirection of the clad 4 is substantially the same as the width in thex-axis direction of the semiconductor laser 1 and the nonlinear material7. The wing sections 13 diffuse the spontaneous emission light N in thex-axis direction or transmit the spontaneous emission light N to theoutside.

FIG. 10 is a b-b′ sectional view of FIG. 9. As shown in FIG. 10, thewidth in the x-axis direction of the clad 4 is smaller than the width inthe x direction of the laser medium 5 and the like. The wing sections 13are formed between the laser medium 5 and the bonding agent 3 andarranged to be close to the sides extending in the z-axis directionamong the sides of the clad 4. Consequently, the wing sections 13 areformed in a flat shape having principal planes in planes same as theprincipal planes of the clad 4. The principal plane width on the uppersurface side of the laser medium 5 is larger than the principal planewidth of a bonding surface bonded with the clad 4. In the solid-statelaser element 60, the laser medium 5 operates as a core in the xz planeand forms a waveguide.

The wing sections 13 allow the spontaneous emission light N in thex-axis direction to escape to the outer side of the laser medium 5 ordiffuse the spontaneous emission light N. Therefore, the spontaneousemission light N deviates from the total reflection condition for thewaveguide and leaks to the outside of the waveguide. Consequently, theamplification of the spontaneous emission light N in the x-axisdirection decreases. Therefore, even when the semiconductor laser 1having large width in the x-axis direction or the semiconductor laser 1in which a plurality of active layers 1 a are arranged is used as anexcitation source, parasitic oscillation and extraction of energy due tothe amplification of spontaneous emission light decrease.

FIG. 11 is an enlarged view (1) of a B section shown in FIG. 10. FIG. 12is an enlarged view (2) of the B section shown in FIG. 10. In FIG. 11,the B section shown in FIG. 10 is shown as a solid-state laser element61. In FIG. 12, the B section shown in FIG. 10 is shown as a solid-statelaser element 62.

The wing section 13 of the solid-state laser element 61 shown in FIG. 11is a roughened surface 13 a of the laser medium 5 that transmits a partof the spontaneous emission light N while diffusing the same andreflects a part of the spontaneous emission light N while diffusing thesame. In other words, a section (the wing section 13) not bonded to theclad 4 in the lower surface of the laser medium 5 is roughened to formthe roughened surface 13 a in the wing section 13.

In this case, a part of the spontaneous emission light N entering theroughened surface 13 a side (the spontaneous emission light N in thex-axis direction, etc.) is reflected on the roughened surface 13 a whilebeing diffused. Further, a part of the spontaneous emission light Nentering the roughened surface 13 a side is transmitted through theroughened surface 13 a while being diffused and travels to the outerside of the laser medium 5. A part of the spontaneous emission light Ndiffused by the roughened surface 13 a deviates from the totalreflection condition for the waveguide. Therefore, parasitic oscillationand the spontaneous emission light N to be amplified decrease.

The wing section 13 of the solid-state laser element 62 shown in FIG. 12is a reflection preventing film 13 b that transmits the spontaneousemission light N. In other words, the reflection preventing film 13 b isdisposed in the section not bonded to the clad 4 in the lower surface ofthe laser medium 5.

In this case, the spontaneous emission light N entering the reflectionpreventing film 13 b side is transmitted through the reflectionpreventing film 13 b and travels to the outer side of the laser medium5. Consequently, parasitic oscillation and the spontaneous emissionlight N to be amplified decrease.

In the explanation of this embodiment, the width in the x-axis directionof the heat sink 2 and the bonding agent 3 is the same as the width inthe x-axis direction of the laser medium 5. However, the width in thex-axis direction of the heat sink 2 and the bonding agent 3 can be thesame as the width in the x-axis direction of the clad 4.

An absorbent (Cr⁴⁺:YAG, carbon, etc.) for the spontaneous emission lightN can be bonded to the wing section 13 instead of the reflectionpreventing film 13 b. In this case, the upper surface side of the wingsection 13 is not limited to the laser medium 5 and can be the absorbentfor the spontaneous emission light N.

FIG. 13 is an enlarged view (3) of the B section shown in FIG. 10. FIG.14 is an enlarged view (4) of the B section shown in FIG. 10. In FIG.13, the B section shown in FIG. 10 is shown as a solid-state laserelement 63. In FIG. 14, the B section shown in FIG. 10 is shown as asolid-state laser element 64.

The wing section 13 of the solid-state laser element 63 shown in FIG. 13and the wing section 13 of the solid-state laser element 64 shown inFIG. 14 are absorbents 13 c and 13 d that absorb the spontaneousemission light N. In FIG. 13, the absorbent 13 c is disposed in thesection not bonded to the clad 4 in the lower surface of the lasermedium 5. In FIG. 14, the absorbent 13 d is disposed on a side of thelaser medium 5 and a side of the clad 4.

In the solid-state laser elements 63 and 64, the spontaneous emissionlight N entering the absorbents 13 c and 13 d side is absorbed by theabsorbents 13 c and 13 d. Consequently, parasitic oscillation and thespontaneous emission light N to be amplified decrease.

The wing section 13 can be disposed on the upper surface side of thelaser medium 5 or can be disposed on both the upper surface side and thelower surface side of the laser medium 5. The principal plane of theroughened surface 13 a is not limited to be present in a surface same asthe upper surface of the clad 4 (in a case where positions in the y-axisdirection are same each other) and can be present further on the lowerside or the upper side than the upper surface of the clad 4.

As explained above, according to the second embodiment, the wingsections 13 diffuse the spontaneous emission light N in the x-axisdirection or transmit the spontaneous emission light N to the outer sideof the laser medium 5. Therefore, the parasitic oscillation indirections other than the optical axis 6 direction and the extraction ofenergy due to the amplification of the spontaneous emission light Ndecrease, and the decrease in the gain in the optical axis 6 directionis reduced. Therefore, the solid-state laser element 60 can output ahigh-power laser.

Third Embodiment

A third embodiment of the present invention is explained with referenceto FIG. 2 and FIGS. 15 to 20. In the third embodiment, wing sections 14explained later obtained by forming grooves in the laser medium 5 aredisposed on outer sides in the x-axis direction of the clad 4 as meansfor allowing the spontaneous emission light N to escape to the outsideof the laser medium 5 (transmitting or absorbing the spontaneousemission light N) or means for diffusing the spontaneous emission lightN.

FIG. 15 is a top view of the configuration of a wavelength conversionlaser device according to the third embodiment of the present invention.Components that attain functions same as those of the wavelengthconversion laser device 101 according to the first embodiment shown inFIG. 1 and the wavelength conversion laser device 102 according to thesecond embodiment shown in FIG. 9 among components shown in FIG. 15 aredenoted by the same numerals and redundant explanation of the componentsis omitted.

A wavelength conversion laser device 103 of the plane waveguide typeincludes the semiconductor laser 1, the nonlinear material 7, and asolid-state laser element 70 as a main characteristic of the presentinvention. In the solid-state laser element 70, the laser medium 5operates as a core in the xz plane and forms a waveguide.

The wavelength conversion laser device 103 performs laser oscillationand performs wavelength conversion for a fundamental wave laser beamaccording to processing same as that performed by the wavelengthconversion laser device 101. In this embodiment, the width in the x-axisdirection of the laser medium 5 is set larger than the width in thex-axis direction of the clad 4. The wing sections 14 are respectivelyformed further on outer sides in the x-axis direction than the clad 4(near the sides perpendicular to the end faces 5 a and 5 b). The wingsections 14 are formed on the upper side of the clad 4 and arranged tobe close to the sides extending in the z-axis direction among the sidesof the laser medium 5. The wing sections 14 are formed in a flat shapeparallel to the xz plane. Principal planes thereof viewed from the uppersurface are formed in a substantially rectangular shape.

The length in the optical axis 6 direction of the wing sections 14 islength substantially the same as the length in the optical axis 6direction of the principal planes of the laser medium 5. In the wingsections 14, areas of the laser medium 5 and areas of a roughenedsurface 20 are alternately arranged in the optical axis 6 direction.Consequently, the wing sections 14 are formed in a comb tooth shapeobtained by arranging a plurality of roughened surfaces 20 in the lasermedium 5. The roughened surfaces 20 are formed on groove wall surfacesformed to cut into the laser medium 5 (groove wall surfaces formed toextend in the principal plane width direction). In other words, groovewall surfaces formed in the laser medium 5 (boundary surfaces betweengrooves and the laser medium 5) among grooves of the comb tooth shapeformed in the wing sections 14 are the roughened surfaces 20. The wingsections 14 diffuse the spontaneous emission light N in the x-axisdirection in the wing sections 14 with the roughened surfaces 20.

The wing sections 14 diffuse the spontaneous emission light N in thex-axis direction with the roughened surfaces 20. Therefore, because thespontaneous emission light N deviates from the total reflectioncondition for the waveguide and leaks to the outside of the waveguide,the amplification of the spontaneous emission light N in the x-axisdirection decreases. Therefore, even when the semiconductor laser 1having large width in the x-axis direction or the semiconductor laser 1in which a plurality of active layers 1 a are arranged is used as anexcitation source, parasitic oscillation and extraction of energy due tothe amplification of the spontaneous emission light N decrease.

FIG. 16 is an enlarged view of a C section shown in FIG. 15. The wingsection 14 of the solid-state laser element 70 includes the roughenedsurfaces 20 that transmit a part of the spontaneous emission light Nwhile diffusing the same and reflect a part of the spontaneous emissionlight N while diffusing the same. In other words, a section not bondedto the clad 4, which is a section in which the groove wall surfaces areformed, in the lower surface of the laser medium 5 is roughened to formthe roughened surfaces 20 in the wing section 14.

In this case, a part of the spontaneous emission light N entering thewing section 14 side is reflected on the roughened surface 20 whilebeing diffused. When the spontaneous emission light N reflected on theroughened surface 20 while being diffused collides with anotherroughened surface 20 in the wing section 14, the spontaneous emissionlight N is reflected on the other roughened surface 20 while beingdiffused. A part of the spontaneous emission light N entering theroughened surface 13 a side is transmitted through the roughened surface20 while being diffused and travels to the outer side of the lasermedium 5. The spontaneous emission light N repeats the reflection on theroughened surface 20 and the transmission through the roughened surface20 while the spontaneous emission light N propagates through the wingsection 14. A part of the spontaneous emission light N diffused andreflected on the roughened surface 20 deviates from the total reflectioncondition for the waveguide. Consequently, parasitic oscillation and thespontaneous emission light N to be amplified decrease.

FIG. 17 is a c-c′ sectional view (1) of FIG. 15. FIG. 18 is a c-c′sectional view (2) of FIG. 15. FIG. 19 is a c-c′ sectional view (3) ofFIG. 15. In FIGS. 17 to 19, the solid-state laser element 70 shown inFIG. 15 is shown as solid-state laser elements 71 to 73, respectively.The roughened surfaces 20 shown in FIG. 15 are shown as roughenedsurfaces 20 a to 20 c, respectively.

In the solid-state laser element 71 shown in FIG. 17, the roughenedsurfaces 20 a are disposed such that the height in the y-axis directionof principal planes of the roughened surfaces 20 a (upper surfacesformed in the xz plane) is between the upper surface and the lowersurface of the laser medium 5. Sides of the roughened surfaces 20 a(sides formed in the yz plane) are disposed to be located in surfacessame as the sides of the clad 4. In the solid-state laser element 71,the lower surface side of the wing section 14 is drilled to form theroughened surfaces 20 a. Consequently, the roughened surfaces 20 a havesections parallel to the xz plane, sections parallel to the yz plane,and sections parallel to the xy plane. Because the grooves formed in thewing section 14 reach the lower surface side of the clad 4, roughenedsurfaces corresponding to lower surfaces of the grooves are not present.

In the solid-state laser element 72 shown in FIG. 18, sides of roughenedsurfaces 20 b are disposed to be located in surfaces same as the sidesof the clad 4 (in the yz plane). Consequently, the roughened surfaces 20b have sections parallel to the yz plane and sections parallel to the xyplane. Because the grooves formed in the wing section 14 reach the lowersurface side of the clad 4, roughened surfaces corresponding to lowersurfaces of the grooves are not present. Because the grooves formed inthe wing section 14 reach the upper surface side of the laser medium 5,roughened surfaces corresponding to upper surfaces of the grooves arenot present.

In the solid-state laser element 73 shown in FIG. 19, sides of theroughened surfaces 20 c are disposed to be located in surfaces same asthe sides of the clad 4. Consequently, the roughened surfaces 20 c havesections parallel to the yz plane and sections parallel to the xy plane.Because the grooves formed in the wing section 14 reach the uppersurface side of the clad 4, roughened surfaces corresponding to lowersurfaces of the grooves are not present. Because the grooves formed inthe wing section 14 reach the upper surface side of the laser medium 5,roughened surfaces corresponding to upper surfaces of the grooves arenot present.

When the roughened surfaces 20 a are formed in the wing section 14, theupper surface side of the wing section 14 can be drilled to form theroughened surfaces 20 a or both the upper surface side and the lowersurface side can be drilled to form the roughened surfaces 20 a.

The shape of the grooves is not limited to the rectangular shape viewedfrom the upper surface and can be other shapes. For example, distal endsof the grooves can be tapered by setting the width of the grooves formedon the inner side of the laser medium 5 smaller than the width of thegrooves formed on the outer side of the laser medium 5. The groove wallsurfaces are not limited to straight surfaces and can be curvedsurfaces. Principal planes of the groove wall surfaces can be inclinednot to be parallel to the principal planes of the laser medium 5 or canbe inclined not to be parallel to the end faces 5 a and 5 b of the lasermedium 5.

For example, when the principal planes of the groove wall surfaces areinclined, the principal planes of the groove wall surfaces can beinclined in a longitudinal direction thereof (the x-axis direction) orcan be inclined in a latitudinal direction thereof (the z-axisdirection). When the principal planes of the groove wall surfaces areinclined in the longitudinal direction, the groove wall surfaces inclinelike the inclined sections 12 explained with reference to FIG. 3 in thefirst embodiment.

FIG. 20 is a sectional view of a wing section in which principal planesof groove wall surfaces are inclined in the latitudinal direction. InFIG. 20, a sectional configuration of a side of the solid-state laserelement 70 viewed from the principal plane width direction is shown. InFIG. 20, the solid-state laser element 70 shown in FIG. 15 is shown as asolid-state laser element 74 and the roughened surface 20 shown in FIG.15 is shown as roughened surfaces 20 d.

In the solid-state laser element 74, sides of the roughened surfaces 20d are inclined by a predetermined angle from the y-axis direction not tobe parallel to the y-axis direction. Consequently, the roughenedsurfaces 20 d have sections parallel to the xz plane (principal planesof the groove wall surfaces) and inclined sides (inclined surfaces).

Because the roughened surfaces 20 d incline in the principal planedirection of the laser medium 5, when the spontaneous emission light Nis made incident on the roughened surfaces 20, the roughened surfaces 20d reflect this spontaneous emission light N to the principal plane sideof the laser medium 5. Therefore, when the groove wall surfaces areinclined, roughened surfaces do not have to be formed on the groove wallsurfaces.

Grooves can be formed in the laser medium 5 such that sides of adjacentgrooves among the groove wall surfaces are non-parallel to each other.FIG. 21 is a sectional view of a wing section in which sides of adjacentgrooves are non-parallel to each other. In FIG. 21, a top view of thesolid-state laser element 70 is shown. In FIG. 21, the solid-state laserelement 70 shown in FIG. 15 is shown as a solid-state laser element 75and the roughened surfaces 20 shown in FIG. 15 are shown as roughenedsurfaces 20 e. When the grooves are disposed such that the sides of thegrooves are non-parallel to each other, the spontaneous emission light Nin the x-axis direction tends to deviate from the total reflectioncondition for the waveguide. Therefore, parasitic oscillation and thespontaneous emission light N to be amplified decrease. In this way, theshape of the grooves can be, for example, pole shapes such as a squarepole shape, a triangular pole shape, and a columnar shape or can be apyramid shape, a triangular pyramid shape, and a conical shape.

The configuration of the roughened surface 13 a, the reflectionpreventing film 13 b, and the absorbents 13 c and 13 d explained withreference to FIGS. 11 to 14 in the second embodiment can be applied tothe solid-state laser element 70 shown in FIG. 15. In this case, theroughened surface 13 a and the reflection preventing film 13 b areformed in positions corresponding to the lower surfaces of the grooves.

The configuration of the inclined sections 12 explained with referenceto FIG. 3 in the first embodiment can be applied to the solid-statelaser element 70 shown in FIG. 15. In this case, the inclined sections12 are formed by inclining sections other than places where the groovesare formed in the wing sections 14.

As explained above, according to the third embodiment, the wing sections14 transmit a part of the spontaneous emission light N while diffusingthe same and reflect a part of the spontaneous emission light N whilediffusing the same with the roughened surfaces 20. Therefore, theparasitic oscillation in directions other than the optical axis 6direction and the extraction of energy due to the amplification of thespontaneous emission light N decrease, and the decrease in the gain inthe optical axis 6 direction is reduced. Because a plurality of groovesof the roughened surfaces 20 and the like are arranged in a comb toothshape in the laser medium 5, the spontaneous emission light N in thex-axis direction can be efficiently diffused. Therefore, the solid-statelaser element 70 can output a high-power laser.

Fourth Embodiment

A fourth embodiment of the present invention is explained with referenceto FIG. 22. In the fourth embodiment, a pair of wing sections areprovided on both the sides of the laser medium 5 by extending the lasermedium 5 in the principal plane width direction such that the sides ofthe laser medium 5 are non-parallel to each other.

FIG. 22 is a top view of the configuration of a wavelength conversionlaser device according to the fourth embodiment of the presentinvention. Components that attain functions same as those of thewavelength conversion laser device 101 according to the first embodimentshown in FIG. 1 among components shown in FIG. 22 are denoted by thesame numerals and redundant explanation of the components is omitted.

A wavelength conversion laser device 104 of the plane waveguide typeincludes the semiconductor laser 1, the nonlinear material 7, and asolid-state laser element 80 as a main characteristic of the presentinvention. In the solid-state laser element 80, the laser medium 5operates as a core in the xz plane and forms a waveguide.

The wavelength conversion laser device 104 performs laser oscillationaccording to processing same as that performed by the wavelengthconversion laser device 101 and performs wavelength conversion for afundamental wave laser beam. In the laser medium 5, when the width inthe x-axis direction is fixed (when the sides are parallel to eachother), the spontaneous emission light N tends to be amplified.

Therefore, in this embodiment, the laser medium 5, the width in thex-axis direction of which is not fixed, is disposed. Specifically, thewidth in the x-axis direction of the laser medium 5 is partiallyincreased to prevent the width in the x-axis direction of the lasermedium 5 from becoming narrower than the width in the x-axis directionof a LD-beam emitting surface of the semiconductor laser 1 and the endface 7 b of the nonlinear material 7. Consequently, the principalsurfaces of the laser medium 5 are formed in a trapezoidal shape or thelike to prevent the sides of the laser medium 5 (the sides other thanthe end faces 5 a and 5 b) from becoming parallel to each other.

Because the sides of the laser medium 5 are not parallel to each other,the spontaneous emission light N in the x-axis direction deviates fromthe total reflection condition for the waveguide. Consequently, theamplification of the spontaneous emission light N in the x-axisdirection decreases. Therefore, even when the semiconductor laser 1having large width in the x-axis direction or the semiconductor laser 1in which a plurality of active layers 1 a are arranged is used as anexcitation source, the parasitic oscillation and the extraction ofenergy due to the amplification of the spontaneous emission lightdecrease.

In the explanation of this embodiment, the sides of the laser medium 5are straight surfaces. However, the sides of the laser medium 5 can becurved surfaces. The inclined sections 12 explained in the firstembodiment, the wing sections 13 explained in the second embodiment, thewing sections 14 explained in the third embodiment, and the like can bedisposed on the sides of the laser medium 5.

As explained above, according to the fourth embodiment, the sides of thelaser medium 5 are disposed in non-parallel to each other. Therefore,the parasitic oscillation in directions other than the optical axis 6direction and the extraction of energy due to the amplification of thespontaneous emission light N decrease, and the decrease in the gain inthe optical axis 6 direction is reduced. Therefore, the solid-statelaser element 80 can output a high-power laser.

The substrate 11 (the substrate 11 including the reflection preventingfilm 15 and the roughened surface 16) explained with reference to FIGS.6 to 8 in the first embodiment can be disposed in the solid-state laserelements 60 to 80 according to the second to fourth embodiments.

INDUSTRIAL APPLICABILITY

As explained above, the solid-state laser element according to thepresent invention is suitable for laser output performed by using theplane waveguide.

1. A solid-state laser element of a plane waveguide type that causes afundamental wave laser beam to oscillate in a beam axis direction in alaser medium of a flat shape and forms a waveguide structure in athickness direction as a direction perpendicular to a principal plane ofthe flat shape in the laser medium, the solid-state laser elementcomprising: inclined sections that are provided on both sides of thelaser medium and inclined a predetermined angle to reflect spontaneousemission light in the laser medium to a principal plane side of the flatshape, the spontaneous emission light traveling in the beam axisdirection and a principal plane width direction as a directionperpendicular to the thickness direction.
 2. The solid-state laserelement according to claim 1, wherein the inclined sections are mirrorsurfaces that reflect the spontaneous emission light.
 3. The solid-statelaser element according to claim 1, wherein the inclined sections areroughened surfaces that diffuse and transmit a part of spontaneousemission light and diffuse and reflect a part of the spontaneousemission light.
 4. The solid-state laser element according to claim 1,further comprising a substrate that is disposed on a reflectingdirection side of the spontaneous emission light by the inclinedsections and bonded to the principal plane of the laser medium via apredetermined bonding surface, wherein an opposed surface of thesubstrate opposed to the bonding surface is a transmissive surface thattransmits the spontaneous emission light from the inclined sections. 5.The solid-state laser element according to claim 1, further comprising asubstrate that is disposed on a reflecting direction side of thespontaneous emission light by the inclined sections and bonded to theprincipal plane of the laser medium via a predetermined bonding surface,wherein the substrate is the roughened surface.
 6. A solid-state laserelement of a plane waveguide type that causes a fundamental wave laserbeam to oscillate in a beam axis direction in a laser medium of a flatshape and forms a waveguide structure in a thickness direction as adirection perpendicular to a principal plane of the flat shape in thelaser medium, the solid-state laser element comprising: wing sectionsthat are provided on both sides of the laser medium and are parallel tothe principal plane of the flat shape to allow spontaneous emissionlight in the laser medium to escape to an outer side of the lasermedium, the spontaneous emission light traveling in the beam axisdirection and a principal plane width direction as a directionperpendicular to the thickness direction.
 7. The solid-state laserelement according to claim 6, wherein the wing sections include thelaser medium extended in directions of the both sides, and atransmissive surface disposed on the extended laser medium to transmitthe spontaneous emission light.
 8. The solid-state laser elementaccording to claim 6, wherein the wing sections include the laser mediumextended in directions of the both sides, and a roughened surfacedisposed on the extended laser medium to diffuse and transmit a part ofthe spontaneous emission light and diffuse and reflect a part of thespontaneous emission light.
 9. The solid-state laser element accordingto claim 6, wherein the wing sections include absorbents that are bondedto the laser medium on the both sides to absorb the spontaneous emissionlight.
 10. The solid-state laser element according to claim 6, whereinthe wing sections include the laser medium extended in directions ofboth the sides, and an absorbent that is disposed on the extended lasermedium to absorb the spontaneous emission light.
 11. A solid-state laserelement of a plane waveguide type that causes a fundamental wave laserbeam to oscillate in a beam axis direction in a laser medium of a flatshape and forms a waveguide structure in a thickness direction as adirection perpendicular to a principal plane of the flat shape in thelaser medium, the solid-state laser element comprising: wing sectionsthat are provided on both sides of the laser medium and that allowspontaneous emission light in the laser medium to escape from groovewall surfaces of grooves formed to extend in the principal plane widthdirection in the laser medium to an outer side of the laser medium, thespontaneous emission light traveling in the beam axis direction and aprincipal plane width direction as a direction perpendicular to thethickness direction.
 12. The solid-state laser element according toclaim 11, wherein a plurality of the grooves line up in a directionparallel to the principal plane of the flat shape to be formed in a combtooth shape.
 13. The solid-state laser element according to claim 11,wherein the groove wall surfaces are inclined surfaces inclined apredetermined angle from a direction parallel to the principal plane ofthe flat shape to reflect the spontaneous emission light in the lasermedium to a principal plane side of the flat shape, the spontaneousemission light traveling in the principal plane width direction.
 14. Thesolid-state laser element according to claim 11, wherein the groove wallsurfaces are formed such that sides of the grooves adjacent to eachother are non-parallel to each other.
 15. The solid-state laser elementaccording to claim 11, wherein the groove wall surfaces are roughenedsurfaces that diffuse and transmit a part of the spontaneous emissionlight and diffuse and reflect a part of the spontaneous emission light.16. A solid-state laser element of a plane waveguide type that causes afundamental wave laser beam to oscillate in a beam axis direction in alaser medium of a flat shape and forms a waveguide structure in athickness direction as a direction perpendicular to a principal plane ofthe flat shape in the laser medium, the solid-state laser elementcomprising: a pair of wing sections that are provided on both sides ofthe laser medium and that reflect spontaneous emission light in thelaser medium into the laser medium, the spontaneous emission lighttraveling in the beam axis direction and a principal plane widthdirection as a direction perpendicular to the thickness direction,wherein the pair of wing sections are the laser medium extended indirections of the both sides such that sides of the laser medium arenon-parallel to each other.